When designing and operating a new residential home, the designers of the home and its heating, ventilating, and air conditioning (HVAC) systems seek to maintain a minimum air change per hour (ACH) rate of at least 0.35 ACH to maintain a healthy environment for occupants.
The ACH rate may be influenced by the ventilation airflow rate of outside air that is introduced into the space by the HVAC system by, for example, outside air intakes. The infiltration rate is another variable that influences the ACH rate. The infiltration rate is the volumetric flow rate of outside air into a building such as for example, a residential or commercial structure through windows, doors, passive ventilation, and other openings in the space. The infiltration rate may be added to the ventilation airflow rate to approximate the ACH of a space. The ventilation airflow rate should be balanced with the infiltration rate to maintain a minimum desired ACH while avoiding reducing the efficiency of the system by introducing unnecessary amounts of outside air. For example, an increased ventilation rate of about 0.10 ACH can increase annual heating energy consumption and cost by about 10%.
Previous methods for calculating the infiltration rate of a space or structure include performing a blower door test that may be performed by a technician using specialized equipment.